This invention relates to electrical components packaged in land grid array (LGA) modules, and more particularly to an apparatus and method for performing electrical testing of LGA modules.
The actual working elements of modern electronic and electrical devices often take the form of small electronic chips, that are mounted individually, or with other chips, inside of a module having a closed housing that protects the chips from environmental damage, and provides input/output connections to a circuit incorporating the module.
One commonly used type of module, known as a land grid array (LGA) module, is shown in FIGS. 1A and 1B. The LGA module 10 of FIGS. 1A and 1B includes a housing, having a substrate 12 and a cover 18. The substrate 12 has an upper surface for receiving the chips, and a bottom, flat, planar surface 14 having plurality of LGA electrical contacts 16 arranged in an array as shown in FIG. 1B. Such LGA modules 10 may include more than one thousand LGA electrical contacts 16. The top of the substrate 12 is closed, or xe2x80x9ccappedxe2x80x9d by joining the cover 18 to the substrate 12 with an adhesive or solder. The cover 18 includes recesses for the chips on the side of the cover 19 joined to the substrate 12
Such LGA modules 10 are typically connected to a circuit card having an array of electrical contacts corresponding to at least a portion of the LGA electrical contacts, by positioning a device known as an interposer 20, as shown in FIGS. 2A and 2B, between the LGA module 10 and the circuit card, and clamping the LGA module 10 and interposer 20 to the circuit card. There are several types of interposers 20 that are typically used for this purpose.
One commonly used type of interposer 20 includes a molded body having a raised frame 19 surrounding a flat planar surface 21 that includes an array of through holes 22. The through holes 22 are aligned with the arrays of LGA electrical contacts 16 on the LGA module 10 and circuit card, and with respect to a pair of location holes 26 passing through the raised frame 29. As shown in FIG. 2B, each hole 22 in the interposer 20 includes a compressible electrically conductive element 24, such as a pad of kinked small diameter wire, a C-spring that is compressed when the LGA module 10 is clamped to the circuit card, to provide electrical contact between the LGA electrical contacts 16 and the circuit card.
In a second type of commonly used interposer 20, the flat planar surface 21 of the interposer 20 is provided by a thin sheet of electrically insulative material, such as a polyimide, that is attached to the raised frame 19. The sheet of polyimide material includes through holes 22 aligned with the arrays of LGA electrical contacts 16 on the LGA module 10 and circuit card, and with respect to a pair of location holes 26 passing through the raised frame 29, in the same manner as described above with respect to an interposer 20 having a molded body. In the second type of interposer, however, each hole includes a compressible electrically conductive element 24 formed from a conductive elastomeric material, such as a silver-filled silicone.
The clamping force for holding the LGA module 10 against the circuit card is typically provided by a clamping device having a number of metal plates, stiffeners, tension posts, and a spring element, all held together by one or more screws, in a relationship that applies a clamping force to the LGA module 10. The clamping device may also include a heat exchanger for dissipating heat generated during operation of the LGA module. These clamping devices are often complex in nature to ensure that the clamping pressure is applied uniformly to the LGA module 10, for optimal electrical contact with the circuit card and optimal thermal transfer to the heat exchanger.
The electrical performance of LGA modules varies somewhat from module to module, due to slight variations in the performance of the chips, and factors relating to the installation of the chips in the modules that cannot be controlled during fabrication of the module. As is the case in many electronic components, an initial burn in period is also required in some instances to screen out certain defective modules and ensure that the completed modules will not fail prematurely. As a result, it is often necessary to test completed LGA modules prior to installing them into a circuit to determine their individual performance, or to burn in the modules at various operating voltages, clock speeds, and power levels, while the module is operating in a known temperature range.
It is desirable that an apparatus and method for testing the LGA modules be capable of closely emulating the physical mounting arrangement that will be used for attaching the LGA module to a circuit card during actual use of the module. While it would appear to be desirable to utilize the actual clamping hardware for testing the module, i.e. the hardware that will be used for mounting the LGA module on a circuit card in an electronic device, such hardware is typically not capable of being conveniently and repeatedly installed and removed in the manner that would be required for the mounting hardware to function as a test apparatus. Such hardware is typically designed to be so compact and light weight that it does not lend itself well to repeatedly establishing clamping and electrical connection conditions that are uniform enough, from module to module, to serve as a basis for testing.
In addition, a typical set of clamping hardware does not include a heat exchanging device that is sophisticated enough to allow testing of the module under a variety of environmental temperature conditions. The heat sinks used in such clamping arrangements are generally designed to operate only in the specific application and operating environment that the module will encounter during actual operation, and do not allow the module to be tested at higher or lower operating temperatures.
In a test apparatus, it is highly desirable to rapidly apply a clamping force to the cover 18 of the LGA module during testing, for clamping the LGA module against a circuit card, with a device such as an air or hydraulic cylinder or an arbor press, having a ram element that can be quickly moved along a one dimensional axis. Unfortunately, the upper surface of the cover 18 is typically not parallel to the bottom, flat, planar surface 14 of LGA module and the electrical contacts 16. If a one dimensional force is applied directly to the cover 18, using the ram element, the LGA electrical contacts 16 will not be clamped with uniform force against the circuit card. If the contacts 16 are not clamped with a uniform force, the electrical conductivity of the contacts 16 will not be uniform or representative of what will be achieved in service, thereby introducing an unacceptable variable into the test results. Also, if the upper surface of the cover 18 is tilted slightly with respect to the lower surface of the LGA module 10, good thermal contact will not be achieved between a heat exchanger clamped against the cover 18 by the ram element, thereby making it difficult to precisely control temperature of the LGA module 10 during testing and burn-in of the module.
What is needed is an apparatus and method for effectively and efficiently testing and burning-in LGA modules.
Our invention provides an apparatus and method for effectively and efficiently testing land grid array (LGA) modules in a mounting arrangement that closely matches the actual mounting arrangement that will be used for attaching the LGA modules to a circuit card, through the use of a self-aligning clamping device for clamping the LGA against a circuit card. The self-aligning clamping device includes a clamping body having an LGA contact surface adapted for bearing against the LGA module, and a pivot element for receiving a clamping force from a ram element selectively movable along a ram axis oriented generally normal to the array of electrical test contacts on the circuit card and transferring the clamping force to the clamping body. The clamping body may also be a heat exchanger for maintaining the LGA module at a desired operating temperature during test or burn-in.
In one form of our invention, an apparatus is provided for testing an (LGA) module having a flat planar mounting surface including a plurality of LGA electrical contacts arranged in an array. The apparatus includes a support frame, a circuit card, a ram element, and a self-aligning clamping device. The circuit card has a flat planar surface attached to the support frame and having an array of electrical test contacts corresponding to a portion of the array of LGA electrical contacts disposed on the planar surface. The ram element is operatively attached to the support frame for selectively applying a clamping force through reciprocating movement of the ram element along a ram axis oriented generally normal to the array of electrical contacts on the flat planar surface of the circuit card. The self-aligning clamping device includes a clamping body having an LGA contact surface adapted for bearing against the LGA module, and a pivot element operatively attached to the ram element for receiving the clamping force and transferring the clamping force to the clamping body. The pivot element may provide a single point of contact for transferring the clamping force to the clamping body. The pivot element may apply the clamping force along a primary line of force that is directed through a centroid defined by the LGA electrical contacts.
The apparatus may include an interposer positioned on the circuit card for receiving the LGA module. By using the same type of interposer in the test apparatus that will be used for attaching the LGA module to a circuit card when the module is placed into actual service, the electrical contact conditions established during testing closely approximates the conditions that will be established when the module is attached to a circuit card and placed into service. The apparatus may include an LGA socket retention frame for positioning the interposer and LGA module on the circuit card, so that the interposer can be conveniently replaced from time-to-time during testing quantities of the modules.
The apparatus may include a force generating device, such as an air or hydraulic cylinder, or an arbor press, operatively connected through the ram element to the pivot element for applying the clamping force to the clamping body. The clamping body may also be a heat exchanger for exchanging heat with the LGA module.
To facilitate achieving a uniform clamping force applied to the LGA module, the self-aligning clamping device may bring the LGA contact surface of the clamping body to bear against the LGA module and align the LGA contact surface with the LGA module prior to the clamping body receiving and transferring the clamping force to the LGA module.
The self-aligning clamping device may include a suspension plate adapted for receiving the clamping force, and having a first pivot element extending therefrom. A second pivot element is attached to the clamping body. One or more suspension posts slidingly connect the clamping body to the suspension plate in a spaced relationship therewith in a manner allowing angular movement over a predetermined range of the clamping body with respect to the suspension plate. One or more spring elements may be operatively connected between the suspension plate and clamping body for maintaining the spaced relationship while allowing angular movement within the predetermined range between the clamping body and suspension plate. The first pivot element may have a convex spherical shape, and the second pivot element may be a flat plate.
Our invention may also take the form of method for testing an LGA module by positioning the LGA module on a circuit card having an array of electrical test contacts corresponding to a portion of the array of LGA electrical contacts, and clamping the LGA module against the circuit card with a self-aligning clamping device including a clamping body having an LGA contact surface adapted for bearing against the LGA module, and a pivot element for receiving a clamping force from a ram element selectively movable along a ram axis oriented generally normal to the array of electrical test contacts on the circuit card and transferring the clamping force to the clamping body.
The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of our invention rather than limiting, the scope of our invention being defined by the appended claims and equivalents thereof.